A single core processor system operates at night, as a power conservation technique, in a low power consumption mode where the system operated at a slower clock speed. For example, a printer performs a print job such as the time-specified printing at night in a low power consumption mode (hereinafter, “related art 1”) (see, for example, Japanese Laid-open Patent Publication No. 2002-86844).
A multiple-core processor system has divided a process performed by one application into multiple segments and used multiple central processing units (CPU) to perform the process in parallel, thereby enhancing the performance. Therefore, the application runs faster.
The multiple-core processor system consumes more power when multiple CPUs perform a process in parallel than when one CPU performs the process. When high performance is desired more than power conservation, it is better to perform parallel processing with multiple CPUs. On the other hand, when high performance such as a shorter processing time is not required, some CPUs may be turned off to reduce the number of CPUs so that power consumption is reduced.
In a cellular phone, processes such as updating of software or self-checking of the system are performed automatically in the background aside from a phone call, email, or a browser which a user activates. Recently, as a cellular phone system becomes more complicated, the automatic background processes are increasing. However, many of the background processes are not urgent.
Unlike the case of the printer, there will be a user who uses a cellular phone at night. Some user may use the device frequently at night. Therefore, the reduction of CPUs during a fixed time period such as night lowers the performance if the user frequently operates the device during that time period.
Even in the daytime, some user does not use the device. Thus, the activation of many CPUs in the daytime wastes the power.